Pd(ii) nanoparticles in porous polystyrene: Factors influencing the nanoparticle size and catalytic properties

Article abstract of DOI:10.1039/c2jm30634d

In this paper for the first time we present a systematic study of the influence of hydrophobicity of Pd(ii) compounds, (CH₃CN) ₂PdCl₂, (PhCN)₂PdCl₂, (Sty)(CH ₃CN)PdCl₂, and (StyPdCl₂)₂, on nanoparticle (NP) formation in the pores of hydrophobic micro/mesoporous hypercrosslinked polystyrene (HPS). The morphology and composition of HPS-Pd nanocomposites were studied using transmission electron microscopy, X-ray fluorescence measurements, X-ray photoelectron spectroscopy, and liquid nitrogen physisorption. The size and location of Pd compound NPs were found to depend on hydrophobicity of the Pd(ii) environment. Catalytic testing of these nanocomposites in d-glucose oxidation was carried out to illustrate the influence of nanoparticle size and environment on catalytic activity. The highest catalytic activity was achieved for (Sty)(CH₃CN)PdCl ₂, forming smallest NPs and allowing an optimal hydrophobicity- hydrophilicity balance with HPS. The Royal Society of Chemistry 2012.

Full text of DOI:10.1039/c2jm30634d

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PAPER
Pd(II) nanoparticles in porous polystyrene: factors influencing the nanoparticle
size and catalytic properties†
Irina B. Tsvetkova,a Valentina G. Matveeva,b Valentin Y. Doluda,b Alexei V. Bykov,b Alexander I. Sidorov,b
Sergey V. Schennikov,b Michael G. Sulman,bc Pyotr M. Valetsky,c Barry D. Stein,d Chun-Hsing Chen,a
b
Esther M. Sulman and Lyudmila M. Bronstein
a
*
Received 2nd February 2012, Accepted 3rd February 2012
DOI: 10.1039/c2jm30634d
In this paper for the first time we present a systematic study of the influence of hydrophobicity of Pd(II)
compounds, (CH3CN)2PdCl2, (PhCN)2PdCl2, (Sty)(CH3CN)PdCl2, and (StyPdCl2)2, on nanoparticle
(NP) formation in the pores of hydrophobic micro/mesoporous hypercrosslinked polystyrene (HPS).
The morphology and composition of HPS–Pd nanocomposites were studied using transmission
electron microscopy, X-ray fluorescence measurements, X-ray photoelectron spectroscopy, and liquid
nitrogen physisorption. The size and location of Pd compound NPs were found to depend on
hydrophobicity of the Pd(II) environment. Catalytic testing of these nanocomposites in D-glucose
oxidation was carried out to illustrate the influence of nanoparticle size and environment on catalytic
activity. The highest catalytic activity was achieved for (Sty)(CH3CN)PdCl2, forming smallest NPs and
allowing an optimal hydrophobicity–hydrophilicity balance with HPS.
porous hydrophobic solids using wet impregnation,14–16 however,
1. Introduction
in our opinion, in order to form regular NPs in a hydrophobic
mesoporous matrix, metal compounds should possess certain
hydrophobicity. In a recent work it was reported that when polar
metal compounds are used (i.e., tetraammineplatinum(II)
nitrate), the particles are not well dispersed in the mesoporous
carbon and large particles (20 nm or more) are formed.17 When
a more hydrophobic precursor was used (platinum(II) acetyla-
cetonate), the deposition of Pt(II) inside the hydrophobic meso-
pores was regular.17
One of the most common methods of nanoparticle (NP) incor-
poration in mesoporous solids is direct impregnation of meso-
porous materials with metal compounds followed by reduction,
oxidation, thermal decomposition, UV-irradiation or ultrasonic
treatment.1–3 The NP size may depend on the amount of metal
compound, conditions of further treatment, pore size, etc. It is
noteworthy that catalytic NPs are not necessarily metal or metal
oxide NPs, but can be also unchanged molecular precursor
(metal salt or complex) NPs which are directly used in catalysis
or converted to catalytic species during reaction.4 The majority
of mesoporous materials employed are metal oxides, i.e., SiO2,
Al2O3, ZrO2, TiO2, etc.5–9 All these materials are sufficiently
polar (hydrophilic) and compatible with common metal salts,
therefore the latter can be uniformly incorporated in these solids.
The typical non-polar (hydrophobic) mesoporous solids are
mesoporous carbons10,11 and hydrophobic nanoporous polymers
such as hypercrosslinked polystyrene (HPS).12,13 Similar to
mesoporous oxides, metal compounds can be incorporated into
In this paper for the first time we present a systematic study of
the influence of Pd(II) compound nature on the size of NPs
formed in a hydrophobic micro/mesoporous material, hyper-
crosslinked polystyrene (HPS) as illustrated in Scheme 1.
HPS is the first representative of cross-linked polymers
characterized by unique porosity.12,13 Due to its high cross-
linking density (which can exceed 100%), HPS consists of rigid
pores, the sizes of which depend on the preparation conditions.
The commercial HPS18 is designed to contain micropores and
small and large mesopores or even macropores for better mass
transport.19 These porous polymers have a large inner surface
area (usually nearly 1000 m2 gꢀ1) and the ability to swell in
nearly any liquid medium, revealing promising properties for
nanoparticle formation. In our preceding work the HPS
samples containing micro/macro- or mesopores were success-
fully used as a polymeric matrix controlling NP formation and
as a carrier of catalytic NPs.19–22 Because the catalytic properties
of NPs are size dependent,23–25 narrow particle size distribution
and an optimal particle size (often between 1 and 3 nm) are
desired.26
aIndiana University, Department of Chemistry, Bloomington, IN 47405,
USA. E-mail: lybronst@indiana.edu; Fax: +1-812-855-8300; Tel: +1-
812-855-3727
bTver State Technical University, Department of Biotechnology and
Chemistry, 22 A. Nikitina St, 170026 Tver, Russia
cA.N. Nesmeyanov Institute of Organoelement Compounds, 28 Vavilov St.,
Moscow 119991, Russia
dIndiana University, Department of Biology, Bloomington, IN 47405, USA
† Electronic supplementary information (ESI) available: A synthetic
procedure, TEM, XPS, and N2 adsorption–desorption isotherms. See
DOI: 10.1039/c2jm30634d
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2.2. Synthesis of styrene Pd complexes
Styrene–palladium chloride was prepared following the method
described elsewhere.41 Bis(benzonitrile) palladium chloride (0.1 g,
0.26 mM) was dissolved in 4 mL of benzene and the solution was
filtered. Then 2.6 mM (0.3 mL) of styrene was added to the
solution and precipitation occurred rapidly. The product was
collected by centrifugation and washed with diethyl ether three
times. After drying in a vacuum oven for 1 hour, styrene–palla-
dium chloride was analyzed by 1H NMR and elemental analysis.
1H NMR (CDCl3) of (C8H8PdCl2)2: 7.51 (br. s, 4H, Ar), 7.36
(br. s, 6H, Ar), 6.94 (br. m., 2H, PhCH), 5.60 (br. m., 2H, cis to
Ph), 5.20 (d, 2H, J ¼ 10.2, trans to Ph).
Elemental analysis data. Calculated, %: C 34.14; H 2.86; Cl
25.19; Pd 37.81; found, %: C 34.7; H 3.4; Cl 25.40; Pd 36.7.
A mixed (styrene–acetonitrile) complex was prepared by
employing bis(acetonitrile) palladium chloride as a starting
material. Bis(acetonitrile) palladium chloride (0.1 g, 0.4 mM) was
suspended in 1 mL of styrene (8.7 mM) and stirred for 2 hours.
After that the product was separated by centrifugation, washed
twice with acetone and dried in a vacuum oven. The product was
analyzed by 1H NMR and elemental analysis.
1H NMR (CDCl3) of (C8H8)(C2H3N)PdCl2: 7.47 (br. s, 2H,
Ar), 7.33 (br. s, 3H, Ar), 6.86 (br. m., 1H, PhCH), 5.64 (br. m.,
1H, cis to Ph), 5.22 (d, 1H, J ¼ 10.2, trans to Ph); 1.98 (s, 3H,
CH3).
Scheme 1 Schematic depiction of incorporation of Pd complexes in HPS
depending on hydrophobicity–hydrophilicity balance: I for low to
medium hydrophobicity and II for high hydrophobicity.
Pd nanoparticles are commonly used in hydrogenation of
unsaturated compounds, for example, cyclohexene,27–29 1,3-
cyclooctadiene and 1,3-cyclohexadiene,27 methyl methacrylate,30
and allyl alcohol31,32 and in catalytic oxidation of sugars
including D-glucose.33,34 Pd(II) compounds also show catalytic
activity in oxidation of various sugars.35–37 In this work to
illustrate the influence of nanoparticle size and environment on
catalytic properties, micro/mesoporous HPS containing four Pd
compounds of different hydrophobicity were tested in catalytic
oxidation of D-glucose to D-gluconic acid (DGA) (Scheme S1,
ESI†). This reaction is both a model for selective oxidation of an
aldehyde group to a carboxyl one and of practical importance:
DGA serves as an intermediate in calcium gluconate, calcium
pangamate and gluconolactone syntheses.38–40 The influence of
hydrophobicity of Pd(II) compound nanoparticles on structure
and composition of HPS–Pd samples was studied here using
transmission electron microscopy (TEM), X-ray fluorescence
(XRF) measurements, X-ray photoelectron spectroscopy (XPS),
and liquid nitrogen physisorption. We demonstrated that the
highest catalytic activity is achieved for (Sty)(CH3CN)PdCl2,
forming smallest NPs and allowing an optimal hydrophobicity–
hydrophilicity balance with HPS.
Elemental analysis data. Calculated, %: C 37.24; H 3.44; Cl
21.98; N 4.34; Pd 33.00; found, %: C 38.4; H 4.3; Cl 22.44; N 4.1;
Pd 31.9.
2.3. Incorporation of Pd compounds in HPS
In a typical procedure, a predetermined amount of a palladium
compound (Table 1) was dissolved in 2 mL of CHCl3 to allow
a final palladium content in a polymer matrix of 1.5%. HPS
(0.5 g) was placed in a Schlenk tube, dried under vacuum for
2 hours and filled with argon afterwards. The degassed solution
of the palladium compound was added to the Schlenk tube by
a syringe through the rubber septum in the argon flow at room
temperature. After that the HPS sample was allowed to swell for
30 min in the solution, the excess solvent (if any) was evacuated
under vacuum and dried in vacuum overnight.
2. Experimental part
2.1. Materials
2.4. Oxidation of D-glucose
HPS was purchased from Purolite Int. (UK), as Macronet MN
270/3860 type 2/100 (designated as MN-270). The size of the
MN-270 granules is 50–70 micrometres. The granules were
washed with acetone and water twice and dried under vacuum
The catalytic reaction was carried out by the method described
elsewhere.42 It was conducted batchwise in a PARR 4200 appa-
ratus which provides independent control over parameters such
as D-glucose and NaHCO3 concentrations, catalyst concentra-
tion, temperature, pure oxygen feed rate, oxygen pressure, and
stirring rate. A suspension of the catalyst and an aqueous solu-
tion of D-glucose (20 mL) prepared at a predetermined concen-
tration were placed in the reactor. An equimolar quantity of the
alkalizing agent (NaHCO3) was fed to the apparatus continu-
ously over 720 min (to maintain pH in the range 6.0–7.5), using
an automatic dispenser. The high-stirring rates employed here
ensured good mixing without diffusion limitation. Probes of the
reaction mixture were periodically removed for analysis. At the
end of each experiment, the catalyst was separated by filtration
for
24
hours.
Bis(benzonitrile)
palladium
chloride
((PhCN)2PdCl2, 95%), bis(acetonitrile) palladium chloride
((CH3CN)2PdCl2, 99%), styrene (Sty, $99%), sodium carbonate
(Na2CO3, $99.0%), sodium bicarbonate (NaHCO3, $99.5%),
and tetrahydrofuran (THF, >99.9%) were purchased from
Sigma-Aldrich and used as received. D-Glucose ($99%) was
bought from Sigma and used without purification. Reagent
grade oxygen of 98.4% purity was received from local oxygen
purification station. Distilled water was purified with an Elsi-
Aqua water purification system.
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Table 1 Palladium content and nanoparticle sizes, D, in the HPS–Pd samples prepared with different Pd compound precursors
Pd compound
loading/g
Standard
deviationb (%)
Sample notation
Metal compound
Pd content (wt%)a
D/nmb
HPS–Pd1
HPS–Pd2
HPS–Pd3
HPS–Pd4
(CH3CN)2PdCl2
(PhCN)2PdCl2
(Sty)(CH3CN)PdCl2
(StyPdCl2)2
0.018
0.027
0.023
0.020
1.18
1.05
1.30
1.19
5.4
3.9
2.2
—
33
23
19
—
a
From XRF measurements. b From TEM data.
and the filtrate was analyzed to measure the content of D-glucose
and of the sodium salt of D-gluconic acid by HPLC.
HPLC analysis was carried out using an Ultimate 3000 HPLC
chromatograph equipped with an RI detector, stainless steel
column 250 mm ꢁ 2 mm (Supelcogel-Ca) characterized by
64 000 theoretical plate number. The phosphate buffer (pH 7.6)
with a space velocity of 0.5 ml minꢀ1 at 50 ꢂC was used as
a mobile phase.
2.5. Characterization
XRF measurements to determine the Pd content (Table 1) were
performed with a Zeiss Jena VRA-30 spectrometer (Mo anode,
LiF crystal analyzer and SZ detector). Analyses were based on
the Co Ka line and a series of standards prepared by mixing 1 g
of polystyrene with 10–20 mg of standard compounds. The time
of data acquisition was constant at 10 s. Elemental analysis for C,
H, and N was carried out by combustion.
Fig. 1 TEM images of HPS–Pd1 (a), HPS–Pd2 (b), HPS–Pd3 (c), and HPS–Pd4 (d) from Table 1.
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X-Ray photoelectron spectra were obtained using Mg Ka
(hn ¼ 1253.6 eV) radiation with a ES-2403 spectrometer
(provided by the Institute for Analytic Instrumentation of the
Russian Academy of Sciences, St. Petersburg, Russia) equipped
with the energy analyzer PHOIBOS 100-MCD5 (SPECS, Ger-
many). All data were acquired at an X-ray power of 100 W.
Survey spectra were recorded at a step of 0.5 eV with analyzer
pass energy 40 eV, and high resolution spectra were recorded at
a step of 0.05 eV with analyzer pass energy 7 eV. Samples were
allowed to outgas for 60 min before analysis and were sufficiently
stable during examination.
demonstrate the striking differences in the morphology of the
NPs formed.
3.1. Morphology of HPS–Pd samples
Fig. 1 shows TEM images of four HPS–Pd samples prepared by
impregnation of HPS with the above Pd compounds. Diameters
of the Pd compound NPs and the standard deviations are pre-
sented in Table 1. The NP sizes decrease from 5.4 nm to 3.9 nm
and to 2.2 nm for (CH3CN)2PdCl2, (PhCN)2PdCl2, and
(Sty)(CH3CN)PdCl2, respectively, thus revealing that the NP size
is directly dependent on the Pd(II) environment (see path I in
Scheme 1). The hydrophobicity–hydrophilicity balance is hardly
quantifiable for HPS–Pd materials discussed in this paper, but we
suggest considering two factors. One of them is polarity of the
ligands surrounding the Pd(II) center which can be quantified
using dielectric constants of ligands. The other factor is a quali-
tative estimation of hydrophobicity using molecular structures of
Pd compounds presented in Fig. 2–4.
Nitrogen physisorption was conducted at the normal boiling
point of liquid nitrogen using a Beckman Coulter SA 3100
apparatus (Coulter Corporation, Miami, Florida). Prior to the
analysis, samples were degassed in a Beckman Coulter SA-PREP
apparatus for sample preparation (Coulter Corporation, Miami,
ꢂ
Florida) at 120 C in vacuum for 1 h.
TEM was performed with a JEOL JEM1010 transmission
electron microscope operated at an accelerating voltage of 80 kV.
Pd-containing HPS powders were embedded in epoxy resin and
subsequently microtomed at ambient temperature. Images of the
resulting thin sections (ca. 50 nm thick) were collected with the
Gatan digital camera and analyzed with the Adobe Photoshop
software package and the ImageJ software. Typically, 50 to
70 NPs were used for analysis.
The dielectric constants of acetonitrile, benzonitrile, and
styrene are 36.64, 25.9, and 2.47, respectively.44 We surmise that
the more polar ligands allow less compatibility with HPS, thus
3. Results and discussion
In order to understand the influence of the Pd precursor nature
on NP formation in HPS, we systematically changed the Pd(II)
environment increasing hydrophobicity of the ligands for
otherwise similar compounds. It is noteworthy that HPS is
extremely hydrophobic but, due to unusual porosity and high
cross-linking density, it can accommodate even quite hydrophilic
compounds. We believe the behavior of any compound incor-
porated into a porous matrix depends on its ability either to
spread along the pore walls, when both the matrix and the metal
compound have similar properties, or to be repelled by the pore
walls (when both are especially dissimilar). This leads to
formation of particles of different sizes and with different loca-
tions depending on the metal compound properties. Therefore,
metal compound behavior in HPS depends on the hydropho-
bicity–hydrophilicity balance between the metal compound and
HPS. To investigate this property, we used two commercially
available Pd compounds, (CH3CN)2PdCl2, and (PhCN)2PdCl2,
and synthesized two more, in one case, replacing one acetonitrile
ligand in (CH3CN)2PdCl2 by styrene, (Sty)(CH3CN)PdCl2, and
in the other case, having two styrene ligands attached to a binu-
clear PdCl2 complex, (StyPdCl2)2. The latter compound was
synthesized according to the published procedure (see the
Experimental part).41 For (Sty)(CH3CN)PdCl2, the 1H NMR
and elemental analysis data confirm the presence of both aceto-
nitrile and styrene in 1 : 1 ratio. At the same time, these data do
not match chemical shifts of either (CH3CN)2PdCl2 (ref. 43) or
(StyPdCl2)2 (see the Experimental part) indicating that it is not
a mixture of (CH3CN)2PdCl2 and (StyPdCl2)2. Thus, we suggest
that indeed we synthesized a mixed ligand styrene–acetonitrile
palladium chloride. In the next section, we will discuss the
structure of the compounds used, but first we would like to
Fig. 2 Structures of (CH3CN)2PdCl2 (a) and (PhCN)2PdCl2 (b) from the
Cambridge Structural Database (CSD).45
Fig. 3 Proposed chemical (left) and molecular (right) structures of
(Sty)(CH3CN)PdCl2.
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larger NPs should form, due to self-selective ‘‘segregation’’, than
in the case of less polar ligands. At the same time, the polarity of
the whole Pd complex is also dependent on the position of the
ligands in the complex.
Comparison of the (CH3CN)2PdCl2 and (PhCN)2PdCl2
structures presented in Fig. 2 shows that both the complexes
form symmetrical structures with weak intermolecular hydrogen
bonding. Based on their structures, one can conclude that
hydrophobicity of the compound periphery is higher for
(PhCN)2PdCl2 than that of (CH3CN)2PdCl2 because benzoni-
trile is less polar than acetonitrile. It means that (CH3CN)2PdCl2
is less compatible with HPS than (PhCN)2PdCl2, thus for the
former, larger particles should form as confirmed in Fig. 1.
Replacement of one polar CH3CN molecule with hydrophobic
styrene in (Sty)(CH3CN)PdCl2 makes it nonsymmetric with
a suggested structure presented in Fig. 3 (left). Unfortunately, to
the best of our knowledge no molecular structure of this
compound is available in any XRD database and we were unable
to grow a crystal of this compound. Based on a suggested
structure, however, we surmise that in a hydrophobic environ-
ment of HPS this compound should be prone to the formation of
reverse micelles similar to other amphiphiles46 (Fig. 3, right),
exposing sparsely distributed hydrophobic styrene moieties
towards the HPS pore walls. Therefore, this compound should be
more hydrophobic (due to hydrophobic styrene exterior) than
both (CH3CN)2PdCl2 and (PhCN)2PdCl2 and more compatible
with HPS, yielding smaller NPs with a narrower particle size
distribution (Table 1). It is remarkable that in the case of
(StyPdCl2)2 whose observed structure with densely packed are-
nes is presented in Fig. 4, the compatibility with HPS is so high
that no particles are formed: (StyPdCl2)2 evenly spreads along
the pore walls making impossible its observation by TEM (path
II in Scheme 1).
Fig. 4 Molecular structure of (StyPdCl2)2 from the CSD.
For comparison, we also synthesized HPS containing fully
hydrophilic Na2PdCl4 NPs whose TEM image is presented in
Fig. 5 High resolution XPS Pd spectra of HPS–Pd2.
Fig. 6 Pore size distributions of mesopores in the parent HPS and HPS–Pd samples.
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Table 2 Surface areas and pore volumes of the HPS and HPS–Pd samples
BET surface
area/m2 gꢀ1
Micropore
volume/mL gꢀ1
Mesopore
volume/mL gꢀ1
Sample notation
Metal compound
Pd content (wt%)
HPS
—
1624
1347
1174
1411
1359
0.26
0.25
0.40
0.45
0.50
0.57
0.45
0.39
0.35
0.35
HPS–Pd1
HPS–Pd2
HPS–Pd3
HPS–Pd4
(CH3CN)2PdCl2
(PhCN)2PdCl2
(Sty)(CH3CN)PdCl2
(StyPdCl2)2
1.18
1.05
1.30
1.19
Fig. S1 (ESI†). The TEM image clearly shows that the NP size
distribution is extremely broad, indicating that in this case, no
control over NP formation takes place.
physisorption. The shape of nitrogen adsorption isotherms
(Fig. S2, ESI†) clearly indicates that all HPS-based samples
contain both micropores and mesopores.47 Fig. 6 demonstrates
that the major fraction of mesopores contains pores with
a diameter of ꢃ4 nm along with larger mesopores with diameters
5–25 nm. The volume fraction of micropores in the parent HPS
and HPS containing (CH3CN)2PdCl2 (which forms largest
5.4 nm NPs, Table 1) remains practically unchanged (Table 2),
indicating that these NPs do not reside in the micropore necks,
and thus do not diminish their fraction. On the other hand, the
fraction of mesopores decreases by 21%, revealing that NPs
block some mesopores. Alternatively, for all other samples with
smaller NPs (3.9 nm for (PhCN)2PdCl2 and 2.2 nm for
(Sty)(CH3CN)PdCl2) or no NPs at all (for (StyPdCl2)2), the
micropore fraction increases, while the mesopore fraction
decreases. This indicates that the smaller NPs reside inside
smaller (ꢃ4 nm) mesopores creating bottle-neck micropores. In
the case of (StyPdCl2)2, the Pd compound spreads along small
mesopore walls, also creating new micropores.
XPS studies of HPS–Pd1–4 samples demonstrated that the Pd
3d5/2 binding energy is nearly the same in all four samples and
measures 337.8–338.7 eV (matching that of the Pd(II) species45),
indicating that incorporation of Pd complexes in the HPS matrix
does not change the Pd oxidation state. The typical high reso-
lution XPS spectrum is shown in Fig. 5.
3.2. Porosity of HPS and HPS–Pd samples
Another important question in structural characterization of the
HPS–Pd nanocomposites is where Pd compound NPs are located
within the porous HPS matrix. This can be deduced from the
analysis of the porosity data.
The porosity of parent HPS as well as the porosity of the HPS–
Pd samples have been evaluated using liquid nitrogen
3.3. Catalytic properties
To illustrate the influence of nanoparticle size and environment
on catalytic properties of HPS–Pd materials, we carried out D-
glucose oxidation under the conditions described in the Experi-
mental part.42
The catalytic curves presented in Fig. 7 show practically no
induction period. The induction period is the catalytic reaction
step when no products are obtained because catalytically active
species are being formed in situ at the beginning of the reaction.48
The length of the induction period may vary from a few minutes
to hours.20,49 The absence of the induction period reveals that
from the beginning of the reaction the Pd compound NPs act as
catalytically active species.
In all the cases, the catalysts exhibited high selectivity in the
range 99.4–99.7% (Table 3) which significantly exceeds that of
the conventional PdCl2 on alumina catalyst (Sigma Aldrich). The
Fig. 7 Dependences of the conversion on time in D-glucose oxidation
with the HPS–Pd catalysts.
Table 3 Catalytic properties of the HPS–Pd samples in oxidation of D-glucosea
Sample notation
Pd compound
Conversion (%)
Selectivity
TOFb ꢁ 104/sꢀ1
HPS–Pd1
HPS–Pd2
HPS–Pd3
HPS–Pd4
Pd/Al2O3 (Sigma Aldrich)
(CH3CN)2PdCl2
(PhCN)2PdCl2
(Sty)(CH3CN)PdCl2
(StyPdCl2)2
69.4
95.4
98.9
72.4
99.2
99.7
99.6
99.4
99.7
89.3
1.4
2.4
3.2
1.6
3.0
—
a
b
Reaction was carried out at 80 ꢂC for 720 min with the ratio [D-glucose]/[catalyst] ¼ 19.5 mol molꢀ1
.
TOF was calculated at 30% conversion; the
experimental error for TOF is ꢄ0.2 ꢁ 10ꢀ4 sꢀ1
.
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4 S. W. Kim and K. D. Kim, Method for Preparing Metal Compound
Nanoparticles, EP 2206681, 2010.
5 C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and
J. S. Beck, Nature, 1992, 359, 710.
6 S. Cabrera, J. El Haskouri, J. Alamo, A. Beltran, D. Beltran,
S. Mendioroz, M. D. Marcos and P. Amoros, Adv. Mater., 1999,
11, 379.
7 H. L. Tidahy, S. Siffert, J.-F. Lamonier, E. A. Zhilinskaya,
A. Aboukais, Z.-Y. Yuan, A. Vantomme, B.-L. Su, X. Canet,
G. De Weireld, M. Frere, T. B. N’Guyen, J.-M. Giraudon and
G. Leclercq, Appl. Catal., A, 2006, 310, 61.
8 L. M. Bronstein, D. M. Chernyshov, R. Karlinsey, J. W. Zwanziger,
V. G. Matveeva, E. M. Sulman, G. N. Demidenko, H.-P. Hentze and
M. Antonietti, Chem. Mater., 2003, 15, 2623.
9 J. H. Schattka, D. G. Shchukin, J. Jia, M. Antonietti and
R. A. Caruso, Chem. Mater., 2002, 14, 5103.
10 C. Vix-Guterl, S. Boulard, J. Parmentier, J. Werckmann and
J. Patarin, Chem. Lett., 2002, 1062.
11 T.-W. Kim, I.-S. Park and R. Ryoo, Angew. Chem., Int. Ed., 2003, 42,
4375.
12 V. A. Davankov and M. P. Tsyurupa, React. Polym., 1990, 13, 27.
13 M. P. Tsyurupa and V. A. Davankov, J. Polym. Sci., Polym. Chem.
Ed., 1980, 18, 1399.
14 J. R. C. Salgado, J. J. Quintana, L. Calvillo, M. J. Lazaro,
P. L. Cabot, I. Esparbe and E. Pastor, Phys. Chem. Chem. Phys.,
2008, 10, 6796.
15 F. Su, L. Lv, F. Y. Lee, T. Liu, A. I. Cooper and X. S. Zhao, J. Am.
Chem. Soc., 2007, 129, 14213.
16 A. B. Fuertes and P. Tartaj, Small, 2007, 3, 275.
17 A. Hayashi, H. Notsu, K. Kimijima, J. Miyamoto and I. Yagi,
Electrochim. Acta, 2008, 53, 6117.
18 L. D. Rampino and F. F. Nord, J. Am. Chem. Soc., 1941, 63, 2745.
19 L. Bronstein, G. Goerigk, M. Kostylev, M. Pink, I. A. Khotina,
P. M. Valetsky, V. G. Matveeva, E. M. Sulman, M. G. Sulman,
A. V. Bykov, N. V. Lakina and R. J. Spontak, J. Phys. Chem. B,
2004, 108, 18234.
high selectivity is normally determined by the optimal sorption–
desorption equilibrium of the reacting and target molecules at
the catalytic center. Apparently for all Pd compounds studied in
this paper, this condition is realized. At the same time, the
activity (TOF, Table 3) of the catalysts is quite different and
clearly dependent on the precursor NPs.
Considering that D-glucose is a hydrophilic substrate, one
might suggest that the best activity should be achieved with more
hydrophilic NPs such as those formed by (CH3CN)2PdCl2 and
(PhCN)2PdCl2, while the worst activity should be found for
(StyPdCl2)2. Indeed the TOF of HPS–Pd4 containing the most
hydrophobic (StyPdCl2)2 complex is low, but even lower TOF
was observed with HPS–Pd1 containing the most hydrophilic
(CH3CN)2PdCl2 NPs. The highest catalytic activity, on the other
hand, was achieved for HPS–Pd3 containing the smallest NPs
with intermediate hydrophobicity. Apparently, for the smallest
NPs the maximum amount of catalytic centers is available for D-
glucose molecules. This allows us to conclude that the NP size
plays the most crucial role in catalyst activity. On the other hand,
the NP size is dependent on the hydrophobicity–hydrophilicity
balance of the Pd complex. In addition, for the (Sty)(CH3CN)
PdCl2 case, hydrophilic D-glucose molecules may penetrate inside
the (Sty)(CH3CN)PdCl2 micelles allowing good compatibility of
the substrate with Pd compound NPs. It is noteworthy that this
TOF is also moderately higher than that of the conventional
PdCl2 on alumina catalyst (Table 3).
4. Conclusions
20 S. N. Sidorov, I. V. Volkov, V. A. Davankov, M. P. Tsyurupa,
P. M. Valetsky, L. M. Bronstein, R. Karlinsey, J. W. Zwanziger,
V. G. Matveeva, E. M. Sulman, N. V. Lakina, E. A. Wilder and
R. J. Spontak, J. Am. Chem. Soc., 2001, 123, 10502.
21 E. Sulman, V. Doluda, S. Dzwigaj, E. Marceau, L. Kustov,
O. Tkachenko, A. Bykov, V. Matveeva, M. Sulman and N. Lakina,
J. Mol. Catal. A: Chem., 2007, 278, 112.
22 A. Bykov, V. Matveeva, M. Sulman, P. Valetskiy, O. Tkachenko,
L. Kustov, L. Bronstein and E. Sulman, Catal. Today, 2009, 140, 64.
23 B. Roldan Cuenya, S.-H. Baeck, T. F. Jaramillo and
E. W. McFarland, J. Am. Chem. Soc., 2003, 125, 12928.
24 J. P. Wilcoxon and B. L. Abrams, Chem. Soc. Rev., 2006, 35, 1162.
25 P. Nowakowski, J.-P. Dallas, S. Villain, A. Kopia and J.-R. Gavarri,
J. Solid State Chem., 2008, 181, 1005.
We demonstrated that the nature of the ligands in the Pd(II)
complexes and their packing in HPS determine formation of Pd
compound NPs including their size and location. The NP size for
the Pd complexes studied decreases with the increase of hydro-
phobicity in the sequence (CH3CN)2PdCl2 > (PhCN)2PdCl2 >
(Sty)(CH3CN)PdCl2. In the case of (StyPdCl2)2 with the highest
hydrophobicity, the compatibility of the complex and HPS is so
high that the former spreads along the HPS pore walls, forming
no NPs. Testing of the catalysts in D-glucose oxidation revealed
that the highest catalytic activity is achieved for (Sty)(CH3CN)
PdCl2, forming smallest NPs and allowing an optimal hydro-
phobicity–hydrophilicity balance with HPS.
26 D. Astruc, F. Lu and J. R. Aranzaes, Angew. Chem., Int. Ed., 2005, 44,
7852.
27 M. V. Seregina, L. M. Bronstein, O. A. Platonova,
D. M. Chernyshov, P. M. Valetsky, J. Hartmann, E. Wenz and
M. Antonietti, Chem. Mater., 1997, 9, 923.
28 A. B. R. Mayer and J. E. Mark, Colloid Polym. Sci., 1997, 275, 333.
29 A. B. R. Mayer, J. E. Mark and R. E. Morris, Polym. J., 1998, 30, 197.
30 Z. Lu, G. Liu, H. Phillips, J. M. Hill, J. Chang and R. A. Kydd, Nano
Lett., 2001, 1, 683.
31 S.-K. Oh, Y. Niu and R. M. Crooks, Langmuir, 2005, 21, 10209.
32 O. M. Wilson, M. R. Knecht, J. C. Garcia-Martinez and
R. M. Crooks, J. Am. Chem. Soc., 2006, 128, 4510.
33 I. V. Delidovich, O. P. Taran, L. G. Matvienko, A. N. Simonov,
I. L. Simakova, A. N. Bobrovskaya and V. N. Parmon, Catal.
Lett., 2010, 140, 14.
34 M. Rosu and A. Schumpe, Chem. Eng. Sci., 2010, 65, 220.
35 A. K. Singh, J. Srivastava, S. Rahmani and V. Singh, Carbohydr. Res.,
2006, 341, 397.
Acknowledgements
This work has been supported in part by the IU Faculty
Research Support Program. The authors also thank the Federal
Program ‘‘Scientists and Educators of Innovative Russia’’ 2009–
20013, contract #14.740.11.0380, the Ministry of Education and
Science of the Russian Federation (grants 16.552.11.7031 and
02.740.11.0864), and funding from the European Community’s
Seventh Framework Programme [FP7/2007–2013] under grant
agreement no. CP-IP 24095.
36 S. Srivastava and P. Singh, Oxid. Commun., 2008, 31, 853.
37 A. K. Singh, T. Gupta, V. K. Singh, S. Rahmani, D. Kesarwani and
B. Singh, Oxid. Commun., 2000, 23, 609.
38 K. B. Kokoh, J. M. Leger, B. Beden and C. Lamy, Electrochim. Acta,
1992, 37, 1333.
Notes and references
1 K. Moller and T. Bein, Chem. Mater., 1998, 10, 2950.
2 L. M. Bronstein, Top. Curr. Chem., 2003, 226, 55.
3 K. Wikander, A. B. Hungria, P. A. Midgley, A. E. C. Palmqvist,
K. Holmberg and J. M. Thomas, J. Colloid Interface Sci., 2007,
305, 204.
39 V. N. Bukin and I. N. Garkina, Method of Producing Calcium
Pangamate, US 3907869, 1975.
This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 6441–6448 | 6447

View Article Online
40 F. Himmelsbach, M. Eckhardt and I. Boehringer, Glucopyranosyl-
Substituted Benzene Derivatives, Medicaments Containing Such
Compounds, their Use and Process for their Manufacture, EP
2360165, 2004.
44 CRC Handbook of Chemistry and Physics: a Ready-Reference Book of
Chemical and Physical Data, ed. D. R. Lide, CRC Press, Boca Raton,
FL, 1999.
45 http://www.ccdc.cam.ac.uk/products/csd/.
41 M. S. Kharasch, R. C. Seyler and F. R. Mayo, J. Am. Chem. Soc.,
1938, 60, 882.
42 E. Sulman, V. Doluda, S. Dzwigaj, E. Marceau, L. Kustov,
O. Tkachenko, A. Bykov, V. Matveeva, M. Sulman and N. Lakina,
J. Mol. Catal. A: Chem., 2007, 278, 112.
46 R. Nagarajan, Curr. Opin. Colloid Interface Sci., 1997, 2, 282.
47 M. Kruk and M. Jaroniec, Chem. Mater., 2001, 13, 3169.
48 S. Shekhar and J. F. Hartwig, Organometallics, 2007, 26, 340.
49 I. B. Tsvetkova, L. M. Bronstein, S. N. Sidorov, O. L. Lependina,
M. G. Sulman, P. M. Valetsky, B. Stein, L. Z. Nikoshvili,
V. G. Matveeva, A. I. T. Sidorov, B. Boris, G. N. Demidenko, L. Kiwi-
Minsker and E. M. Sulman, J. Mol. Catal. A: Chem., 2007, 276, 116.
43 P. A. Dresco, V. S. Zaitsev, R. J. Gambino and B. Chu, Langmuir,
1999, 15, 1945.
6448 | J. Mater. Chem., 2012, 22, 6441–6448
This journal is ª The Royal Society of Chemistry 2012